PROJECT DESCRIPTION Cytomegalovirus (CMV) inflammatory disease of the gastrointestinal tract is a major complication of immunosuppression in Veterans. In addition, CMV can induce relapse, exacerbate mucosal inflammation, and cause glucocorticoid resistance in Veterans with inflammatory bowel disease (IBD). To elucidate the pathogenesis of CMV mucosal inflammation, we have shown that blood monocytes are the exclusive source of intestinal macrophages and that pro-inflammatory monocytes recruited to the gut mucosa differentiate in the presence of extracellular matrix (stroma)-derived TGF-2 into non-inflammatory lamina propria macrophages. In the setting of CMV infection, we hypothesize that (1) CMV infection of monocytes induces resistance to stromal down-regulation; (2) CMV infection of monocytes reverses stromal (TGF-2- mediated) down-regulation by activating NF-:B signaling, resulting in the transcription of pro-inflammatory genes and, after a second stimulus, the release of pro-inflammatory cytokines; and (3) CMV infects intestinal and colonic macrophages and reverses the cells' inflammation anergy. To address these hypotheses, we propose three Specific Aims: (1) Determine whether CMV infection of blood monocytes induces resistance to stromal down-regulation of monocyte pro-inflammatory function. (2) Determine whether CMV infection of blood monocytes and intestinal and colonic macrophages activates NF-:B signal transduction, overriding stromal down-regulation of pro-inflammatory function. (3) Determine whether CMV infection and inflammatory responses in monocytes and intestinal and colonic macrophages are enhanced in the setting of inflamed mucosa. PUBLIC HEALTH RELEVANCE: PUBLIC HEALTH RELEVANCE STATEMENT Birmingham Veterans who undergo organ bone marrow transplantation, acquire HIV-1 infection or develop inflammatory bowel disease (IBD) are vulnerable to cytomegalovirus (CMV) infection. A major target of CMV is the gastrointestinal tract, where the virus can cause inflammatory disease in virtually any organ, resulting in inflammation, ulceration, bleeding and even perforation. In Veterans with IBD, CMV can induce steroid resistance and disease flares. We have shown that pro-inflammatory monocytes, the exclusive source of intestinal and colonic macrophages, differentiate into non-inflammatory intestinal macrophages upon recruitment to the mucosa. However, when the monocytes are infected with CMV, they become resistant to this down-regulation and remain potently pro-inflammatory. This proposal seeks to characterize the mechanism by which CMV promotes pro-inflammatory mucosal macrophages. The goal is to identify potential sites for therapeutic intervention in patients with CMV gastrointestinal disease.